1. Field of the Invention
The Intelligent Systems Division (ISD) has been developing the Stewart Platform parallel-link manipulator for several years. Throughout this development, the ISD has considered a wide variety of cable and support structure configurations within the xe2x80x9cRoboCranexe2x80x9d program. These configurations have been designed to specifically target applications in large-scale manufacturing, waste storage tank remediation, construction, military, and many other applications.
The RoboCrane can control suspended loads, tools and equipment in all six degrees-of-freedom(DOF) without sway or rotations typical of cable suspended systems(e.g., cranes). A spine can be integrated between the platform and support structure to provide constrained motions outside of the typical gravity-forced platform work-volume(e.g., the platform can be pushed to the side using a spine, instead of hanging beneath the upper support points). Control means include independent control of each RoboCrane cable, via a winch and powered by a power amplifier. A computer is used to determine the amount of cable-length to shorten or lengthen based on sensor inputs. As cable lengths are changed, the suspended platform remains fully controllable throughout a very large work volume. This concept is atypical of most robots. Joystick or other computer algorithm commands sent to the RoboCrane can provide complex platform motions controlled throughout the RoboCrane work volume. Pre-programmed trajectories allow the operator to pre-plan RoboCrane motions with updated path information based on sensory interaction with the environment (e.g. maneuvering around an obstacle that was placed in the pre-programmed path of the platform).
The idea of the novel cable configuration from shallow attachment points and modular-configured RoboCrane was first designed and reduced to practice in February 1998. The invention was disclosed to Advanced Technology and Research Corporation (ATR) in a meeting to discuss their interest in reducing the invention to practice on Nov. 9, 1998. A non-disclosure agreement was signed by ATR regarding the invention.
The invention has been publicly disclosed to industry and government participants at an Advanced Double-Hull Shipbuilding Demonstration at the National Institute of Standards and Technology (NIST) on Dec. 3, 1998 and to industry and government participants at a Paint/Depaint Workshop in San Antonio, Tex. on Jan. 12, 1999.
2. Description of Related Art
U.S. Pat. No. 4,666,362 to Landsberger et al. (1987) relates to a Stewart Platform parallel-link manipulator configuration of 6 cables, attached in a xe2x80x9ctripodxe2x80x9d configuration, including a telescoping support spine for the moving platform. Controlling power and motors are hydraulic. Cable lengths are independently controlled via powered spools.
Relevant to the proposed invention, this patent does not claim computer control or sensor integration.
U.S. Pat. No 4,883,184 to Albus (1989) relates to a Stewart Platform parallel-link manipulator configuration of 6 cables attached to a crane with the single crane winch as the lift device of all 6 cables. Cables control attached loads in 6 DOF.
Relevant to the proposed invention, this patent does not claim independent cable length control or sensor integration.
U.S. Pat. No. 5,585,707 to Thompson et al. relates to a tendon suspended platform robot. Claims 1-21 of this patent relate to cable-driven systems suspended from above and tensioned from below as well. Claims 22 through 34 of this patent relate to a cable-driven system suspended from above providing 6 DOF platform motion, on-board winches, position sensing, optical tension sensing, and a controller.
Relevant to the proposed invention, this patent does not claim control using tension feedback from a variable sensor, reconfigurability and adaptability of the suspended platform with a winch, control, and sensor package, various cable configurations with, specifically, 6 and 9 cables providing tendons and platform strength only where needed, or a tension control algorithm to damp platform oscillations, typically due to long cable lengths.
Based on this prior work and ISD research, the RoboCrane includes a variety of configurations and control methods. The new challenge was to create a means for modular robot reconfigurability, simple set-up and calibration, and suspending a moving platform that can carry a robot manipulator or a human worker, or both, throughout a large work volume. Also, the platform needs to apply forces and torques along typical work-volume edges allowing tool control near the attachment points, as well as to be suspended from shallow and widely spaced attachment points without driving cable tensions to exponential extremes.
According to the present invention, these challenges are met by a particularly constructed modular manipulator. The manipulator includes a servo module having a plurality of winches, with corresponding servo axes and winch support structure, sensors, and drive mechanisms by which the winches are independently controlled, and a support which can be suspended from attachment points and which can be positioned at various locations below the attachment points. The winch support structure is attached to the support, and a plurality of cables extends between the attachment points and the winches so as to suspend and position the support below the attachment points. The cables are wound up by and unwound from the winches to position the support at a selected location below the attachment points. The servo module is one of a plurality of servo modules providing for reconfiguration of the servo axes and a variety of cable configurations.
Six, seven, or nine cables may be provided, and the support can be either a platform, with or without a spine, or a spine and a spine bar.
In one configuration, a support spine extends from the platform, nine cables are provided, and three of the nine cables are connected to the support spine to provide added platform constraint. In another configuration, the support is a spine and a spine bar, seven cables are provided, and one cable pair from the seven cables is attached to the spine bar.
The sensors can include absolute position, velocity, and tension sensors, with the tension sensors detecting cable tensions in respective cables. Each tension sensor can be disposed either between the platform and a pulley about which one of the cables passes or between the winch support structure and a winch housing so as to sense cable tension approximately in-line with a respective one of the cables.
A set up and calibration operation can be performed by positioning the platform within a work volume with the cables unwound from the winches to initial cable lengths, setting the cable tensions so that they do not exceed a specified force while being unwound by an operator, connecting a first set of the cables to a first of the attachment points, connecting a second set of the cables to a second of the attachment points, connecting a third set of the cables to a third of the attachment points, and operating the winches so as to raise the platform up off a floor of the work volume. Platform angle and distance values are then input into the controller, and a position of the platform within the work volume is determined from these values.
The drive mechanisms include, for each cable, a winch motor and a brake. A computer reads a desired load velocity and signals from the sensors, combines the desired load velocity with these signals, and computes commands for the winch motor and the brake. This results in production of a desired winch velocity.
The attachment points can be disposed, for example, on any of walls, ceilings, support structures, cranes, bridges, and radio towers. A tool can be attached to an end of a support spine, when such is used, so as to be maneuverable into close tolerance areas. Finally, the manipulator may include an operator interface permitting entry of operator override commands.